The invention relates to the field of cutting coal from a longwall face of a coal vein. More particularly, the invention relates to the detection of lateral and vertical deviations in the movement of a longwall coal shearer which travels along a coal face in a transverse direction for shearing coal from the face.
In longwall mining, the area to be mined is divided into blocks, perhaps 900 feet across and 5,000 feet long. Two access tunnels are cut on either side of a coal block, and a transverse tunnel is cut between access tunnels at one end of the block. A track for a longwall shearer is laid along the coal face or the floor of the tunnel in a manner that enables the coal to be sheared and dumped on a moving conveyor which then removes the coal from the mine. The ceiling along the coal face is held up by hydraulic supports that are moved forward after each cut. After the supports are advanced, the ceiling behind the supports falls in, relieving the roof stresses. Stresses in the mine roof are critical, and to control them the face is kept geometrically normal to the top, bottom, and sides of the coal block being mined. If the face becomes bowed or sheared obliquely, forces on the longwall coal face will become excessive, causing severe loads on the roof supports and making their forward movements difficult if not impossible.
In U.S. Pat. No. 4,156,971, a mechanical system is disclosed by which a longwall shearer is controlled in a path adaptive manner such that it periodically adjusts itself to maintain movement along a desired line of travel. However, this system is machine dependent, and installation requires extensive modification to a standard longwall shearer.
Accordingly, an important object of the present invention is to provide apparatus for guiding a longwall coal shearer which is simple and reliable and is readily adaptable to all models of longwall shearers.
Still another important object of the present invention is to provide apparatus for detecting lateral and vertical deviations in the movement of a longwall coal shearer for a single pass of the machine along the longwall coal face and adjusting the track after one pass to correct for any deviations observed in the prior pass.
Still another important object of the present invention is to provide apparatus for tracking and guiding a longwall shearer which assures a straight cut of the coal face and which is safe and practical under mining conditions utilizing conventional mining equipment.
Still another important object of the present invention is to provide an apparatus for tracking the movement of a longwall coal shearer which utilizes a single light source requiring no sophisticated electronics or specialized lighting equipment.